Pregerminated seeds

ABSTRACT

PCT No. PCT/EP93/02353 Sec. 371 Date Feb. 15, 1995 Sec. 102(e) Date Feb. 15, 1995 PCT Filed Aug. 31, 1993 PCT Pub. No. WO94/05145 PCT Pub. Date Mar. 17, 1994Pregerminated seeds comprising desiccation tolerant emerged radicles, processes for their production, and plants produced from such seeds.

The present invention relates to pregerminated seeds having desiccationtolerant emerged radicles, a process for obtaining such seeds and plantsderived therefrom.

BACKGROUND OF THE INVENTION

Several attempts have been made to produce pregerminated seeds whichgive rise to consistently high and reproducible rates of germination inthe field for many species of plants. However, such attempts have provento be unsatisfactory since inter alia the storage life of such seeds isgenerally of limited duration or requires the employment of specialisedstorage facilities. Furthermore, pregerminated seed has not hithertobeen considered amenable for sowing with conventional sowing methods andequipment i.a.because of the problem of seed dehydration under sowingconditions.

Granted patent specification EP 202879 B1, describes the obtention ofhigh viability seed lots which are selected on the basis of havingemerged radicles which have a moisture content at which radicledevelopment is suspended without loss of seed viability. There is nosuggestion that induction of desiccation tolerance in the radicle isadvantageous and can lead to a product comprising germinated seeds whichare capable of being stored at ambient temperatures for long periods oftime without the need for specialised storage conditions. The highviability seed lots obtainable according to the disclosure of EP 202 879B1 are not desiccation tolerant as indicated by several statements insaid specification and as supported by the examples hereinafterdemonstrating essential differences between the desiccation tolerantpregerminated seeds obtainable according to the teaching of thisinvention and the pregerminated seeds obtainable according to theconditions disclosed in EP 202 879 B1.

Many reports have appeared in the scientific literature of the effectupon seeds or seedlings of desiccation stress. One such report statesthat desiccation tolerance may be due to the presence of disaccharidessuch as sucrose and/or the presence of other plant sugars such asoligosaccharides. However, such a desiccation tolerance in the seed hasbeen observed to be lost upon the emergence of the radicle from the seedcoat and it is at this critical stage of germination that the ability toinduce desiccation tolerance in the radicle has not hitherto beenconsidered practicable [Koster K. L. and Leopold A. C. Plant Physiol.88:829-832 (1988)].

Other workers have reported that maturing Barssica campestris seedacquire desiccation tolerance during seed development and that this hasbeen observed to be concomitant with elevated levels of sucrose content.However, attempts at inducing desiccation tolerance in the emergedradicle of germinated seeds was neither described nor suggested[Leprince O. et al, Plant, Cell, and Environment 13:539-546 (1990)].

The art generally teaches of the loss of desiccation tolerance ingerminated seeds. It has now surprisingly been found that desiccationtolerance can be induced in seeds having an emerged radicle.Furthermore, it has now been found that seeds comprising desiccationtolerant emerged radicles are capable of being sown without the need foremploying refinements to sowing methods such as the application ofencapsulating gels to pregerminated seed and the like. Surprisingly,seeds comprising desiccation tolerant emerged radicles as hereindescribed are capable of being sown using conventional non-germinatedseed sowing methods and equipment without substantial deleterious effecton seed viability.

Advantages of sowing seed in which the radicle has emerged includefaster germination times once sown and provided that the seed suppliercan guarantee a high seed viability per batch of seeds sown, a morereliable estimate of how much seed is required for sowing and hence moreefficient growing methods.

One benefit of inducing desiccation tolerance in the emerged radicle ofpregerminated seeds is that such seeds can be dried back to a moisturecontent approaching that of non-germinated seed. Thus, treated seedcomprising desiccation tolerant emerged radicles is capable of beingstored for long periods of time at ambient temperature i.e. without theneed for employing specialised storage facilities such as refrigerationfacilities and the like.

A further advantage is that seed comprising desiccation tolerant emergedradicles which have not been further dried back can be sown naked i.e.using conventional seed sowing methods and equipment without the needfor employing encapsulating gels and the like.

SUMMARY OF THE INVENTION

An object of the present invention is to provide germinated seedcomprising desiccation tolerant emerged radicles in the form of naked orpelleted seed in commercial quantities suitable for sowing in the field.

Another object is to provide germinated seeds comprising desiccationtolerant emerged radicles which have a long shelf-life and which do notrequire specialised conditions for transport and/or storage.

A further object is to provide a method of treating seed whereindesiccation tolerance is imparted to at least a part of the radicle ofgerminated seed.

These and other objects and advantages of the present invention willbecome apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention there are provided pregerminatedseeds comprising desiccation tolerant emerged radicles.

For the purposes of the present invention the terms `pregerminatedseeds` and `germinated seeds` are used interchangeably and are definedas seeds in which the radicle and/or hypocotyl has protruded or emergedfrom the seed coat or pericarp. The protruded or emerged radicle can besurrounded by endosperm (e.g. Cyclamen) or not depending on species. Thelength of the radicle may be of any length which distinguishesgerminated seed from non-germinated seed. Preferably, the radicle can beof any length up to the maximum diameter of a seed. Thus, where a seedhas an irregular shape, the length of the radicle can approximate thewidest diameter of the seed. The most preferred length for seed coating,sowing and/or separation procedures is of the order of 2.5 mm or lessdepending on seed type. Suitable seed types include those which arecapable of forming root primordia from at least an hypocotyl region;preferred seed types include those types which are not capable ofdeveloping a seminal root system. Examples of this category include allvegetable and flowering species of the types listed in the Handbook forSeedling Evaluation, J.Bekendam and R. Grob ISTA, Zurich, Switzerland1979 on pages 28-29, and especially those types exemplified on pages122-126. Seed types capable of forming roots from an hypocotyl regionare also included within the ambit of the invention. Examples of seedtypes on pages 122-126 of the above reference which may not beconsidered to form a typical seminal root system but which neverthelesscan be said to be capable of forming roots from a hypocotyl regioninclude such seed types as Cyclamen and Impatiens. Preferred seed typesof the invention include those of species representing the groupscomprising Alliums, Antirrhinums, Begonias, Brassicaceae, Capsicums,Betas, Lycopersicons, Cucurbitaceae, Cyclamens, Dianthuses, Gazanias,Gerberas, Impatiens, Lobelias, Nicotianas, Pelargoniums, Petunias,Phloxes, Primulas, Raphanuses, Salvias, Solanaceae, Tagetes, Verbenas,Vincas, Violas, Apiums, Daucuses, Chicoriums, and Zinnias. Mostpreferred seed types include those of species represented by the groupsBrassicaceae, Capsicums, Impatiens, Cyclamens, Petunias, Lycopersiconsand Violas. Also encompassed within the ambit of the present inventionare plants grown from seed as herein described.

The germinated seeds comprising desiccation tolerant emerged radiclesare more versatile than conventional germinated seed because they areable to withstand desiccation stresses imposed by the ambientenvironment which may arise during transport, or on sowing equipment andthe like. Thus, seeds of the invention can also be subjected to furtherdesiccation treatments which can render them storable for longer storageperiods under conventional seed storage conditions relative to seedscomprising emerged radicles which have not been subjected to adesiccation tolerance induction treatment. Conventional seed storageconditions may comprise a relative humidity of from about 30% to 50% anda temperature of from about 15° C. to 20° C. Seed storage conditions mayalso include temperatures within the range of from about -20° C. toabout 25° C. (i.e. room temperature). Alternatively, germinated seeds ofthe invention may be sown using conventional sowing methods andequipment without the need for special treatments such as gelencapsulation for minimising water loss and the like since the seeds canwithstand further desiccation while in situ on seed sowing equipment, inopen sacks and the like.

In another embodiment of the invention there are provided seedscomprising desiccation tolerant emerged radicles which are capable ofbeing sown using conventional sowing equipment.

Typically, germinated seeds of the invention are found to havesubstantially elevated levels of the disaccharide sugar, sucrose intheir radicles, relative to the radicles of germinated seeds which havenot been subjected to a desiccation tolerance treatment as hereindescribed. Naturally, the skilled artisan will appreciate that apregerminated seed in which desiccation tolerance has been induced inthe radicle will also have been rendered desiccation tolerant in otherstructures of the seed, such as for example, in cotyledon structures andthe like.

`Desiccation tolerant` means that the seed radicles in which desiccationtolerance has been induced are capable of withstanding furtherdesiccation treatments which reduce the overall moisture content of theseed to a moisture content typical for that of non-germinated seeds ofthe relevant species without substantially affecting the seeds abilityto resume growth under favourable growing conditions, even after storagefor 1,2 or more weeks. Seeds in which desiccation tolerance has beeninduced in the radicle can be subjected to further desiccationtreatments depending on the objective.

Pregerminated seeds having desiccation tolerant emerged radicles areobtainable by maintaining pregerminated seeds during an incubationperiod at a moisture content sufficiently low to substantially inhibitgrowth of the radicle but high enough to permit other metabolicprocesses to continue. The optimum moisture content will depend on theparticular seed type employed, and can be established by monitoring thedevelopment of metabolic processes in test samples, e.g. sucrose contentincrease during the incubation period. In general, the moisture contentof seeds suitable for desiccation tolerance induction in the emergedradicles will lie in the range of from about 35% to 55%, morespecifically of from about 35% up to about 50% by weight of the seeds.The optimum incubation conditions (incubation time, temperature,relative humidity [RH], osmotic value etc.) can likewise be establishedexperimentally, in that for example the seeds are incubated underdifferent conditions, then dried back to a moisture content typical fornon-germinated seeds and the viability of the dried seeds thenestablished e.g. by determining, for test samples, the percentage ofseedlings obtained after storage for a certain period of time, thepercentage of seeds showing root elongation or secondary root formationetc., as illustrated by the examples hereinafter. In general, theincubation temperature will lie in the range of 0° to 25° C., morepreferably of 0° to 15° C. The incubation period will depend on theother incubation conditions and the particular seed type. In general,satisfactory results are obtained with an incubation period in the rangeof from 1 day to 10 days. Seeds comprising desiccation tolerant emergedradicles which have undergone further desiccation treatments can bestored for longer storage periods under conventional seed storageconditions relative to seeds comprising emerged radicles which have notbeen subjected to a desiccation tolerance induction treatment.Shelf-life of seeds of the invention can thus be lengthened with furtherdesiccation treatments which reduce the overall moisture content of theseed to from about 4% to about 12% by weight of the seed depending onspecies (i.e. moisture content typical for that of non-germinated seedsof the relevant species) which does not substantially affect the abilityof the radicle to resume growth upon the return of favourable growingconditions. A radicle of a seed may be viewed as being desiccationtolerant if it is capable of giving rise to further radicle growtheither in the form of elongation of the primary root per se or formationand/or elongation of root primordia from a point or points located onthe primary root or from the hypocotyl region, after having firstundergone a desiccation tolerance induction treatment. Thus, desiccationtolerance in the emerged radicle may be restricted to at least aparticular part of the emerged radicle, such as the hypocotyl region.

The radicles of germinated seeds having induced desiccation tolerancehave a sucrose content that is elevated relative to the sucrose contentof emerged radicles in seeds of the same species which have notundergone desiccation tolerance induction. Typically, the radicles ofdesiccation tolerant germination seeds have a sucrose content in therange of from about 3% up to about 15% by weight of the radicle.Naturally, the actual sucrose content of the radicle will vary dependingon species. The skilled artisan will appreciate that the overall sucrosecontent of the seed will also increase.

In a further embodiment of the invention there are provided coatedgerminated seeds comprising desiccation tolerant emerged radicles.

`Coated germinated seeds` conforms to the description given above for`germinated seeds` except that the seeds are provided with an additionalprotective layer or in pelleted form. The pelleting material maycomprise any conventional material commonly used in the art forprotecting or pelleting seed. Suitable pelleting materials include clayssuch as sub-bentonite and bentonite, vermiculite along with additivessuch as perlite, pumice, metal stearates, polyethene, polystyrene,polyurethane, talcum powder, polypropene, polyvinyl chloride, starches,loams, sugars, arabic gums, organic polymers, celluloses, flours such aswood flours, quartz powders and the like. Such materials may be added toseed of the invention using conventional layering or pelletingprocedures known in the art. Examples of components which may also beincorporated into the seed coat include growth regulators such asgibberellins or auxins. Typically, the content of growth regulator willbe in the range of from about 0.0001% to about 1.0% by weight of thecoating material.

In a further embodiment there is provided a method of inducingdesiccation tolerance in emerged radicles of germinated seeds comprisingsubjecting germinated seed to environmental conditions conductive to theinduction of desiccation tolerance in the emerged radicle.

In a further embodiment there is provided a method of obtaininggerminated storable seeds comprising desiccation tolerant emergedradicles which comprises

i) subjecting germinated seed to environmental conditions conducive tothe induction of desiccation tolerance in the emerged radicle and

ii) drying back the seed to a moisture content that is substantiallythat of commercially available non-germinated seeds

whereby step (ii) may be initiated before the desiccation toleranceinduction under the conditions of step (i) has been achieved, providedthe drying step (ii) is carried out sufficiently slow to permit the seedradicles to acquire desiccation tolerance before the moisture contenthas reached a level where metabolic processes are substantiallydiscontinued.

In general, the storable germinated seeds according to the inventionwill have a moisture content of from 4% to 12% by weight of the seeds.

The germinated seed used as starting material may be obtained inconventional manner. It will conveniently be obtained by germinatingseed in an appropriate seed germinating environment. A `seed germinatingenvironment` is one wherein seeds may freely germinate at least to theextent that radicle protrusion occurs. The environment must beadequately moist, aerated or oxygenated, and capable of promoting seedgermination to at least the stage of radicle protrusion from the seedcoat or pericarp. An example of such an environment is the aerated watercolumn wherein the degree of aeration is sufficient to keep the seeds ofinterest buoyed or in suspension. The amount of seed per unit volume canbe any suitable amount. A suitable amount can be from 1-200 g seeds/l.In a preferment, the amount of seed does not rise above about 25 gseeds/l of water. The actual amount of seed per unit volume of water isdependent on species. Generally, the temperature of the seed germinatingenvironment is one which permits or promotes the germination of theseed. A suitable temperature of the germinating environment can lie inthe range of from 5° C. to about 30° C. depending on species.Preferably, the temperature of the germinating environment lies withinthe range of from about 15° C. to about 25° C.

Other conventional additions to the germinating environment may includefurther excipients, diluents, additives, factors and regulators asrequired, which may help in promoting or improving germination or ofenhancing secondary root primordia induction in the emerged radicle.Such additions may include but are not limited to the use of plantgrowth regulators or hormones, for example a gibberellin biosynthesisinhibitor such as pactobutrazol (e.g. where it is desired to enhancesurvival of primary roots), a gibberellin (e.g. where it is desired tostimulate secondary root growth) or an auxin which may be added to thegermination environment to a concentration of from about 0.0001% toabout 1.0% by weight of seed germinating environment. Conventionaladditions to the germinating environment also encompasses the use ofphysical stimuli.

Instead of the aerated water column other environments such as moisturefilter paper may be used. Once germination or radicle protrusion fromthe seed coat or pericarp is observed, the germinating seeds areseparated from the others using conventional techniques known in theart. Typically, separation techniques rely on physical differencesbetween germinated seed and non-germinated seed such as size, weight,shape, and the like. An important factor in seed separation is theselection of seed having radicles of the right length. The length of theradicles is preferably up to and including the length or diameter of theseed. Usually, the seeds are surface dried before the induction ofdesiccation tolerance, using procedures commonly employed in the art.

Desiccation tolerance can be induced in the emerged radicle by any oneof several methods. During this induction phase, growth of the radicleis substantially inhibited however the moisture content of the seeds issuch so as to permit other metabolic processes to continue. Suchmoisture content will depend on the particular seed species but will ingeneral not be lower than about 35% by weight of the seed. Some methodsrely on either with-holding water from or with-drawing water from theseed over an `incubation` period. In principle it is sufficient towith-hold water, since the metabolic processes require water and theoverall moisture content of the seeds is reduced when water iswith-held. Thus, the initial moisture content may be equal to that ofgerminating seeds, although a somewhat lower moisture content gives aquicker induction. The aim of the incubation is to place the seed undera mild to moderate water stress.

One method of inducing desiccation tolerance in seeds involves theincubation of seeds comprising emerged radicles for long periods of timeunder conditions wherein moisture loss is prevented. An example is wherethe seeds are held in a closed container such that a minimal exchange ofgases is permitted, for up to several days. For instance such acontainer can be a petri dish with a loose fitting lid, or a largercontainer having a loose fitting lid. The seeds can be incubated at anytemperature within the range of from about 0° C. up to about 25° C.Preferably, seeds are incubated at suitably low temperatures such asfrom about 0° C. to about 15° C., for example, to minimise the risk ofinfestation with pathogens. The period of time and temperature requiredfor incubation may vary from species to species and it may be measuredin terms of days stretching into weeks or longer. Preferably, theincubation period may be any period of time from about 1 day up to about10 days.

In the above case, where a seed coating formulation is to be applied tothe seed, a coating may be conferred on the seed either before or afterthe incubation step and before or after any subsequent drying step.

In a variant of the incubation alternative outlined above, germinatedseeds may first be dried back relatively quickly under conventionaldrying procedures and then submitted to incubation conditions. Thus, themoisture content may initially be reduced to e.g. a moisture contentwhich is about 10% lower than that which germinated seeds normallypossess. Satisfactory results are obtained when the moisture content isbetween about 0.5% to 5% lower, particularly between about 2% and 5%lower than that which germinated seeds normally possess depending onspecies. In general, it is advantageous not to reduce the moisturecontent to less than about 35% by weight of the seeds. For instance, theseeds can be dried back under conditions wherein the temperature lieswithin the range of from 0°-25° C., at a relative humidity within therange of from 30%-90%, in still air or in flowing air at speeds typicalfor drying back seeds. For example the airflow speed may be at any speedup to 2 m/s or faster. The period of time may be for any suitable timeinterval up to about 24 hrs depending on drying conditions employed.Suitable drying conditions are 20 C, at a relative humidity of 40% inair flowing at a speed of 2 m/s over 5 minutes.

Typically, seeds in which desiccation tolerance is to be induced in theradicle are dried back to an overall water content sufficient to permitmetabolic processes to continue but sufficiently below that ofgerminating seed to substantially inhibit radicle growth, typicallyabout 35% to about 55%, more preferably 35% to 50% by weight of the seeddepending on species.

After drying back, the seeds are transferred to an environment whereinmoisture loss is prevented, (e.g. a closed container), and subjected toincubation treatments as described herein before in order to inducedesiccation tolerance in the radicle. As above, where a seed coatingformulation is to be applied to the seed, a coating may be conferred onthe seed either before or after the induction step and before or afterany subsequent drying step.

Water content of seeds or emerged radicles is calculated using thefollowing formula: ##EQU1## where Wi=weight initial

Wa=weight after oven drying seeds or radicles at 103° C. overnight

An alternative method of inducing desiccation tolerance into emergedradicles of seeds includes subjecting such seeds to a water stress viaosmosis. For example, selected seeds may be transferred to an aqueoussolution possessing an osmotic value of from about -0.5 to about -4.0MPa. The actual osmotic value of the solution can vary between species,however, it should be such that growth of the radicle is inhibited butthat the moisture content of the seeds is sufficiently high so as topermit other metabolic processes to continue. In this state seedsexperience a mild water stress due to a lack of availability of freewater. Typically, the seeds are contacted with a solution of a suitableosmoticum such as PEG 8000, mannitol, or a salt solution such as NaCland the like. Plant growth regulators such as methyl jasmonate, andauxins e.g. indole butyric acid (IBA), can also be added to theosmoticum solution at a concentration of between about 0.0001% to about1.0% by weight. Alternatively, seeds may be contacted with a solution ofa suitable plant hormone such as abscisic acid (ABA). Preferably, theseeds are soaked in a suitable osmoticum solution in an aerated columnas hereinbefore described. The actual osmoticum solution used is notcritical to the invention as long as the seeds are not harmed by it. Thecontact time may be for a time interval measured in days extending toweeks or longer, preferably for a period of 1-10 days at a temperaturelying in the range of from 0° to 25° C. More preferably, the contacttime is from 3-10 days. The contact period is preferably carried out ata temperature at less than 10° C. After the contacting period the seedsare washed in water.

After inducing desiccation tolerance in the emerged radicle seedsdestined for storage purposes may be dried back to moisture contentssimilar to those of ungerminated seed eg from about 4% to about 12% byweight depending on species. The method of drying back after inductionof desiccation tolerance in the radicle is not critical provided that asufficient degree of desiccation tolerance has been induced in theradicle and the temperature is not too low. Conveniently the temperatureis not below 10 C. For example in a method of drying, seeds can bespread out in a single layer, and left standing in still air for about24 hrs at a relative humidity of from about 40%-75% and temperature inthe range of from 10°-30° C. After the end of such a drying period,seeds are found to have reached a moisture content of between 4% and 12%by weight, depending on species.

In a further variant, the induction of desiccation tolerance in emergedradicles can be attained and combined with further desiccation in onestep when producing storable seed as mentioned hereinbefore, by dryingback seed comprising emerged radicles very slowly to a moisture contentof ungerminated seed, e.g. of from about 4% to about 12% by weight. Thetime period required for this can be from 2-10 days in duration at arelative humidity lying within the range of from 75% to 90% at atemperature of about 20° C. Preferably the time interval is from about3-7 days under appropriate drying conditions. Appropriate dryingconditions include those temperature conditions as hereinbeforedescribed. Such seeds may then be subjected to further desiccationtreatments depending on design.

Storable seeds are those wherein desiccation tolerance has been inducedin the radicle and which possess a moisture content in the range of fromabout 4% to about 12% by weight. Such seeds can be stored for periods ofat least 3 months in sealed containers such as drums, plastic bags,aluminium-lined bags and the like under storage conditions of theambient environment i.e. without the need for storing in specialisedrefrigeration or cooling conditions, specified temperatures, certainrelative humidity and the like.

There now follow examples which further illustrate the invention. It isto be understood that the examples are not to be viewed as limiting thescope of the invention in any way. The tables referred to in theexamples are shown after Example 14.

EXAMPLE 1

Desiccation tolerance and sucrose content increase during incubation ofgerminated Impatiens seeds in PEG-8000 solution.

25 g seeds of Impatiens (cv Impulse rose, Zaadunie BV) are germinated in2 l of aerated water at 20° C. for 4 days. 3000 germinated seeds areselected, and centrifuged at 1300 rpm for 1 minute to remove excesswater. Seeds are divided into 5 portions of 600 seeds. 4 portions areincubated on blotting paper moistened with a solution of PEG-8000,commercially available from BP Chemicals, Southampton, (324 g/l, waterpotential -1.5 MPa, determined following the teaching of Michel B. E.[(1983) Plant Physiology 72:66-70]), in a closed container at atemperature of 8° C. for periods of 1, 2, 3 or 6 days to inducedesiccation tolerance. One portion is used as a control (i.e.non-incubated). After the induction periods, seeds are rinsed indistilled water. Moisture content of the seeds is determined at the endof the incubation periods and just after rinsing at 44% by weight usingthe formula as herein described.

25 seeds from each portion are used for determining sucrose content atthe end of the incubation periods (i.e. immediately for control seeds),using the UV methodology as outlined in "Methods of Biochemical Analysisand Food Analysis" (1986) pp 96-98 ,Boehringer Mannheim. 100 seeds ofeach portion are sown on soil and the emergence of seedlings is countedafter 14 days.

After rinsing, remaining seeds are dried in still air at 40% relativehumidity (RH) and 20° C., reaching a final moisture content of 5% byweight in 24 hours. Control seeds are dried in the same manner.

After drying, seeds are stored at 40% RH and 20° C. until sowing i.e. 14days after drying of controls.

Table 1 shows that desiccation tolerance developed gradually during theincubation period, the increase in desiccation tolerance coincided withan increase in sucrose content of the seeds.

EXAMPLE 2

Desiccation tolerance and sucrose content increase in pregerminatedtomato seeds.

25 g of tomato seed are germinated in 4 l aerated water at 20° C. After4 days, 1000 seeds with a radicle length of less than the seed diameterare selected by hand. Seeds are blotted dry and placed in a closedcontainer at 8° C. for desiccation tolerance induction periods of 0, 1,4, and 6 days. Moisture content of a sample of 200 seeds is determinedat 48% by weight. After the induction periods the seeds are placed instill air and dried at a temperature of 25° C. and relative humidity of40%. The final moisture content of the seeds is 7% and is reached aftera time interval of about 12 hours. Sucrose content of the emergedradicles is determined at the end of the induction periods, just beforedrying as outlined above. Sucrose content is determined on a sample of50 seeds using the UV methodology described in example 1. After drying,seeds are stored at 40% relative humidity and 25° C. for 14 days. 100seeds from each induction period are planted and percent emergencedetermined after 5 days. Results are shown below in Table 2.

EXAMPLE 3

Slow drying induces desiccation tolerance and elevated sucrose contentin pregerminated Impatiens seeds.

5 g seed of Impatiens seeds are germinated in 4 l water at a temperatureof 20° C. in an aerated column. After 4 days, 1000 germinated seedshaving a radicle length less than that of the seed diameter are selectedby hand. All seeds are centrifuged for 2 minutes at 1300 rpm to removeexcess water.

Seeds are divided into two groups. Seeds of one group are dried at threedifferent drying rates (see below). Seeds of a second group areincubated for 5 days at 8° C. in a closed container. Moisture content ofthe seeds is determined at 47.5% by weight. Seeds are then dried at thesame three different drying rates as the first group.

After drying, seeds are stored at 40% relative humidity and 20° C. for14 days. Sucrose content of the seeds from both groups is determinedafter drying as per example 1. Seeds have a final moisture content of5.5% by weight.

100 seeds from each group are planted and % emergence determined after 7days at 25° C.

Drying Conditions

i) Fast drying

Windspeed 1 m/s at 30% relative humidity and 25° C. Seeds have a finalmoisture content of 5% after 6 hours.

ii) Medium drying

Seeds are placed on trays above a saturated solution of NaCl in achamber (1 m³) having a controlled environment. Windspeed 0.05 m/s.Moisture content is maintained at a relative humidity of 75% andtemperature of 25° C. Seeds are held under these conditions for 24 hoursby which time the seeds reach a moisture content of 10% by weight. Seedsare then transferred to an open container at 40% relative humidity, 20°C. Moisture content is determined at 5% after 24 hours.

iii ) Slow drying

Seeds are placed on petri dishes in a closed container (0.1 dm³)containing a saturated solution of NaCl, at a drying temperature of 25°C. Moisture content above the saturated NaCl solution balances out at arelative humidity of 75% at 25° C. Seeds are held under these conditionsfor 72 hours by which time the seeds reach their final moisture contentof 10%. Seeds are then transferred to an open container at 40% relativehumidity, 20° C. Moisture content is determined at 5% after 24 hours.

Results are shown below in Table 3.

EXAMPLE 4

Shelf-life of Pregerminated Impatiens seeds

20 g seeds of Impatiens (cv Impulse red, Zaadunie BY), (lot 1) and 20 gseeds of Impatiens (cv Impulse scarlet, Zaadunie BY), (lot 2) aregerminated for 4 days in aerated columns in 2 l of water at 20° C. 20 ggerminated seeds having protruding radicles are obtained. Germinatedseeds are selected, and centrifuged (1300 rpm / 1 min) to remove excesswater and incubated for 7 days in a closed container at 8° C. to inducedesiccation tolerance in the emerged radicle. Seeds have a moisturecontent determined at 47% by weight. The seeds are dried in still air,at a relative humidity of 40% and temperature of 20° C. After 48 hoursthe moisture content of the seeds is determined using the formulahereinbefore described, at 5% by weight. Dried seeds are divided up into0.5 g portions which are sealed in aluminium-lined bags. Half of thebags of each seed lot are stored in a cooler at 8° C., the other half ina controlled environment chamber (Van den Berg, Montfoort, NL) at 20° C.Each month a bag is opened and 100 seeds are germinated on moistenedfilter paper at 25° C. in the light. The number of seeds formingsecondary roots after 14 days incubation is counted. Control seedsamples undergo pregermination however a drying step is not included intheir treatment. Controls are stored at 8° C. and 20° C. Results areshown in Table 4.

EXAMPLE 5

A comparison of shelf lives of germinated Impatiens seeds havingdesiccation tolerant emerged radicles (moisture content of 5.0% byweight of seed) and germinated Impatiens seeds not having desiccationtolerant emerged radicles (moisture content of 19.6% by weight of seed).

40 g of Impatiens (cv Blitz salmon, Zaadunie BY) are germinated for 4days in a column in 4 l of aerated water at 20° C. 20 g seeds (approx.20,000 seeds) having emerged radicles are selected. One half of theseeds are dried immediately by first centrifuging at 1300 rpm for 2minutes and then placing them in a plastic box in a fytotron conditionedat 25° C. and 80% RH. After 8 hours the moisture content of the seedsdecreases from an initial 48% by weight to 19.6% by weight. Seeds arethen divided into equal portions and placed in aluminium lined bagswhich are sealed and stored at three temperatures: -20° C., 8° C. and20° C. The other half of the seeds after centrifuging, is incubated inair at 100% relative humidity in a closed container at 8° C. for 7 days,for the induction of desiccation tolerance in the radicle. Moisturecontent at the end of incubation is determined at 46% by weight. Afterincubation, seeds are dried at 25° C. and 80% RH. 24 hours after thestart of drying, seeds are transferred to still air at 40% RH and 20°C., until the final moisture content of the seeds is determined at 5% byweight. Seeds are then divided into equal portions and packed in sealedbags (100 seeds/bag) and stored at -20° C., 8° C. and 20° C.

Immediately after drying and after suitable time intervals in storage,100 seeds are incubated on moistened blotting paper at 25° C. Thepercentage of seedlings having developed secondary roots is determined14 days after the start of incubation. Seeds are also tested forseedling emergence in a soil germination test i.e. 100 seeds are sown insoil at 20° C. and placed under fluorescent light. The percentage ofseedlings is determined 14 days after sowing. Results are shown inTables 5a and 5b.

EXAMPLE 6

A comparison of shelf lives of germinated tomato seeds with desiccationtolerant emerged radicles at 5% moisture content and seeds not havingdesiccation tolerant emerged radicles, 21.6% moisture content.

50 g of tomato seeds (F 7263, experimental variety, Zaadunie BV) aregerminated in a column in 4 l of aerated water at 20° C. 4000 germinatedseeds are selected after 3 days. One half of the germinated seeds aredried immediately by placing them in still air at 75% RH and 20° C. andpermitted to reach a moisture content of 21.6% by weight. Initialmoisture content of the seeds decreases from 50.6% by weight to 21.6% byweight in 6 hours. The other half of the seeds is transferred to acolumn with an aerated solution of PEG-8000, from BP Chemicals, (324 g/l),. Seeds remain in this solution for 7 days at a temperature of 8° C.in order to induce desiccation tolerance in the radicle. The seeds arethen removed, rinsed in distilled water, and moisture content determinedat 46%. Seeds are then dried in still air at 40% RH and 20° C. for 3days. Seed moisture content is then determined to be 5%. Dried seeds ofthe two treatments (18×100 seeds) are then packed separately inaluminium lined bags which are sealed and stored at three temperatures:-20° C., 8° C. and 20° C. After predetermined storage periods, thequality of the seeds is tested by sowing 100 seeds per treatment onsoil. Seeds are sown in trays on soil and placed for three days in thedark at 20° C. before removal to a greenhouse. Percentage of seedlingsis determined two weeks after sowing.

Results in Table 6 show that shelf-life of seeds subjected to adesiccation tolerance induction treatment is longer at all storageconditions tested than for seeds which are directly dried back to amoisture content of 21.6%, and not subjected to a desiccation toleranceinduction treatment.

EXAMPLE 7

A comparison of shelf lives of germinated Brussels sprouts seeds whichhave desiccation tolerant emerged radicles (5% moisture content), andnon-desiccation tolerant seeds having emerged radicles (20% moisturecontent).

100 g of seeds of Brussels sprouts (cv. Tardis, Zaadunie BV) aregerminated in 4 l aerated water at 23° C. After 16 hours germinatedseeds are hand selected. 2100 seeds are selected. Moisture content ofgerminated seeds is determined at 50% by weight. 1000 seeds areincubated on blotting paper moistened with PEG-8000 (BP Chemicals )solution (324 g/l, water potential -1.5 MPa, determined as per example1), at a temperature of 8° C. for 7 days to induce desiccation tolerancein the emerged radicle. Moisture content is determined at 41% by weightat the end of the induction period. Seeds are rinsed in distilled waterand placed in still air at 40% RH and 20° C. until a moisture content of5% is reached after approximately 24 hours. The other 1000 seeds aredried immediately after hand selection in still air at 75% RH and 20° C.until a moisture content of 20.9% is reached after a period of 6 hours.Seeds are then sealed in aluminium lined bags (50 seeds per bag).Packaged seeds are stored at temperatures of -20° C., 8° C. and 20° C.After storage periods of 0, 1 and 2 months 50 seeds per treatment aresown on soil and the percentage of seedlings counted after 10 days.Results are shown in Table 7.

EXAMPLE 8

Seeds of Impatiens, cv Impulse salmon orange, having desiccationtolerant emerged radicles and performance on sowing simulator machines.

50 g of Impatiens, cv Impulse salmon orange are germinated in a columnin 4 l of aerated water at a temperature of 20° C. After 3 days 30 g ofseeds (approx. 30,000 seeds) with emerged radicles are selected.

15 g of seed (control) are placed on a sowing simulator. The other 15 g(test) are incubated in air in a closed container at 100% RH for 7 daysat 8° C. so as to induce desiccation tolerance in the radicle. Moisturecontent of the seeds at the end of the induction step is determined at44.3% by weight. After the induction step, the seeds are sown on asowing simulator as described below.

A simulation of sowing is made on control and test samples by spreadingseeds out in a layer on the bottom of a plastic tray and placing it in afytotron (commercially available from Van den Berg, Montfoort, NL),conditioned at 20° C. and 40% relative humidity. The box is shakenregularly in order to simulate the vibration in the reservoir of asowing machine. At regular intervals a sample of seeds is taken out ofthe tray. 1 g of the sample is used for moisture determination, and 2×50seeds are sown in soil at 20° C. Emergence of the seeds is checked after14 days.

Table 8 shows the advantage of having induced desiccation tolerance inthe emerged radicle of pregerminated seeds over pregerminated seeds nothaving desiccation tolerant emerged radicles.

EXAMPLE 9

Comparison between Tomato seeds having desiccation tolerant emergedradicles and tomato seeds dried under conventional methods.

50 g tomato seeds (F 7263, experimental variety of Zaadunie BY) aregerminated in a column in 4 l of aerated water at 20° C. After threedays germinated seeds are selected and grouped as follows:

Group 1: Control. 500 seeds are placed in still air at a relativehumidity of 40% and at a temperature of 20° C. for 7 days. Moisturecontent of the seeds is determined after 1 day and 7 days to be 6% byweight, respectively. Group 2: Direct drying to 20% by weight formoisture comparison test against seeds of the invention.

500 seeds are placed in still air at a relative humidity of 40% and at atemperature of 20° C. and removed when the moisture content reaches 20%by weight, after 6 hrs. The seeds are then placed in a closed containerfor 7 days at a temperature of 8° C. After this period, seeds aresubdivided into two portions. One portion is placed onto moistenedblotting paper and permitted to imbibe water for 4 days at 25° C. Thesecond portion of seeds is dried back in still air at a relativehumidity of 40% and at a temperature of 20° C. to a moisture content of6%. Group 3: Seeds of the invention.

500 seeds are placed in a petri dish on filter paper moistened inPEG-8000 (BP Chemicals) solution (324 g/l, at a water potential of -1.5MPa determined as per example 1). The petri dish is placed in arefridgerator for 7 days at a temperature of 8° C. to induce desiccationtolerance in the seeds. At the end of the period moisture content of theseeds is determined at 43% by weight. After this period, the seeds arerinsed with distilled water, and seeds are subdivided into two portions.One portion is placed onto moistened blotting paper and permitted toimbibe water for 4 days at 25° C. The second portion is dried back instill air at a relative humidity of 40% and at a temperature of 20° C.to a moisture content of 6%.

Sugar content of embryos is determined using the method of example 1, onthe portion of dried seeds from seed of groups 2 and 3 and on seeds ofgroup 1 after placing them in water for 2 hours and excising 25 embryosper group.

All seed groups (2×100 seeds per group ) are placed on moistenedblotting paper and permitted to imbibe water for 4 days at 25° C.Regeneration of secondary roots is then determined by counting. Resultsare shown in Table 9.

Table 9 shows that seeds of groups 2 and 3 are viable before a dryingtreatment. After a drying treatment seed viability of seeds of group 2is comparable to that of seeds of group 1 which are subjected also to adrying treatment, however, the viability of seeds of the invention,group 3, is higher. Seeds of group 3 are desiccation tolerant.

EXAMPLE 10

Induction of desiccation tolerance in germinated seeds of Cucumber,Viola, and Petunia.

Seeds of cucumber (cv Airaris), Viola (cv Aurora yellow) and Petunia (cvWhite Flash), all of Zaadunie BV, are incubated on moistened filterpaper at 20° C. in petri dishes enclosed in a box. In all cases, 250seeds from each species having protruding radicles are selected after 3days. Seeds of controls are immediately dried in still air at a RH of40% and temperature of 20° C. Seeds of the test samples are incubated onblotting paper moistened with a PEG-8000 solution (324 g/l, at -1.5 MPa,determined as per example 1) for 7 days at 8° C. in a petri-dish undersimilar conditions as described in example 9 to induce desiccationtolerance in the radicle. The seeds are then rinsed in distilled water.Moisture contents after the induction step for cucumber, viola, andpetunia are determined at 46%, 44% and 41% by weight respectively. Thetest samples are then dried in still air at 40% RH and 20° C. for 24hours. 50 dried seeds are incubated on blotting paper moistened withwater, at an ambient temperature of 25° C., and the development ofseedlings is assessed after 14 days.

The sucrose content in cucumber axis and in viola embryos is determinedusing standard procedures (Boehringer-Mannheim supra) before the startof, and at the end of the incubation period. Results are shown in Table10.

Table 10 shows a marked increase in the percentage of seedlings obtainedfrom germinated seeds subjected to a desiccation tolerance treatment.

EXAMPLE 11

Induction of desiccation tolerance in the radicle of Cyclamen.

20 g of Cyclamen (cv. Marion, Zaadunie BY) are germinated in a column in4 l of aerated water in the dark at 18° C. After 7 days 500 seeds areselected at a stage where it is clear that the radicles enclosed inendosperm are protruded from the seed coat i.e. the endosperm bulges outof the seed coat but radicle protrusion from the endosperm is notapparent. Seeds at this stage are either directly dried in still air at40% RH and 20° C. (controls) or seeds (tests) are first incubated beforedrying in a petri dish with blotting paper moistened with a PEG-8000solution at water potential of -1.5 MPa for 7 days following a similarprocedure to that of Group 3 seeds of example 9, in order to inducedesiccation tolerance in the emerged radicle. Moisture content of seedsis determined at the end of the induction period at 42% by weight.

After drying, 100 seeds of control and 100 test seeds are germinated onsoil in the dark at a temperature of 18° C. The percentage of seedlingsis determined 3 weeks after sowing.

The results in Table 11 show that seedling development increasesmarkedly when drying is preceded by an incubation period.

EXAMPLE 12

Induction of desiccation tolerance in pregerminated Capsicum seeds.

5 g of Capsicum seeds (cv Astrion, Zaadunie BV) are incubated in a 4 lcolumn in aerated water at 20° C. for 5 days. Germinated seeds areselected by hand, and divided into three portions of 100 seeds each. Oneportion is placed on a petri dish and dried in still air at 40% Pa, and20° C., to a final seed moisture content of 7%. A second portion isincubated in a petri-dish on filter paper soaked with a solution ofPEG-8000 (324 g/l at -1.5 MPa) for 7 days to induce desiccationtolerance in the emerged radicle. Moisture content of the seeds isdetermined at 45% by weight. Seeds are then dried under the sameconditions as the first portion. The third portion is incubated in aPEG-8000 solution of -1.5 MPa for 7 days, containing indole butyric acid(IBA) at a concentration of 10 μM, to induce desiccation tolerance inthe emerged radicle. Moisture content of the seeds is determined at 45%by weight. The seeds are then dried under the same conditions as forportion 2.

The dry seeds are incubated on moistened filter paper in closedcontainers for 8 days at a temperature of 25° C., and the percentage ofseeds showing regrowth of the primary root recorded after 3 days. Thepercentage of seeds having primary and/or secondary roots is recordedafter 8 days. Results shown in Table 12 indicate that germinatedCapsicum seeds subjected to a desiccation step, survive desiccationconditions and show regrowth of the primary root and/or secondary rootformation. Viability of the root is enhanced after IBA addition.

EXAMPLE 13

Survival of primary roots and growth of secondary roots from thehypocotyl region in tomato depends on length of the radicle, inductionof desiccation tolerance in the radicle.

10 g seeds of tomato (cv. Elena, Zaadunie BY) are incubated on top ofmoistened filter paper at 20 ° C. in the light for 2 days. Half of theseeds are further incubated on filter paper soaked in a solution of 136μM Paclobutrazol, (a synthetic gibberellin biosynthesis inhibitor,commercially available from ICI Plc) at 25° C. The remaining seeds arefurther incubated on moistened filter paper at 25° C. in the light. 600germinated seeds having emerged radicles are selected after 1 day ofincubating at 25 ° C. A selection of 100 seeds having emerged radiclesof 0.5-1.5 mm, and of 100 seeds having emerged radicles of 1.5-2.5 mm ismade. Selected seeds are either immediately dried in still air at 20°C., 40% R.H. for 24 hours to a final seed moisture content of 6%(control), or subjected to a treatment on filter paper moistened with aPEG-8000 solution (324 g/l; -1.5 MPa) at 8° C. for 6 days to inducedesiccation tolerance in the emerged radicle. Moisture content isdetermined at 46% by weight. Seeds are then dried in still air under thesame conditions as for control seeds to the same final seed moisturecontent. After drying, seeds are sown on top of moistened filter paperin closed containers at 25° C., in the light. Survival of the primaryroot is determined visually after 3 days. Survival is defined as primaryroots showing no visible damage and continued growth. Secondary rootformation from an hypocotyl region is measured after 7 days.

Table 13 shows that many emerged radicles die upon desiccation, butdamage is more severe when the radicles are longer in length at the timeof selection. Table 11 further shows that induction of desiccationtolerance results in an increase in survival of primary roots and astimulation of secondary root formation. Treatment with Paclobutrazolresults in a still higher survival of primary roots.

EXAMPLE 14

Incubation of germinated Impatiens seeds in PEG results in increases insucrose content in cotyledons and radicles (hypocotyls) and increaseddesiccation tolerance.

10 g of seeds of Impatiens (cv. Impulse orange, Zaadunie BY) aregerminated in a column containing 4 l of aerated water at 20° C. Afterthree days 1600 germinated seeds are selected. 400 seeds (controls) aredried immediately in still air of 20° C. and 40% RH, and moisturecontent determined at 5% by weight, after 24 hours. 3 batches of 400seeds each are incubated on blotting paper moistened with a solution ofPEG-8000 (324 g/l, water potential at -1.5 MPa) at 8° C., in separateclosed boxes for incubation periods of 1, 2 or 5 days. After incubation,seeds are rinsed in distilled water and blotted dry. Samples of eachtreatment (tests and controls) then undergo a sucrose determination: foreach test and control 25 cotyledon pairs and 100 radicles (hypocotyls)are assessed. Remaining seeds are dried to a moisture content of 5%following the same procedure as for controls. Desiccation tolerance ofdried seeds is assessed by sowing 2×50 seeds from each test and controlon top of paper in the light at a temperature of 25° C. The percentageof seeds which develop into seedlings is assessed 14 days after sowing.

Table 14 shows that during incubation the sucrose content in theradicles rises markedly as does sucrose in the cotyledons. Desiccationtolerance of germinated seeds rises in parallel with elevating sucrosecontent.

                  TABLE 1                                                         ______________________________________                                        Emergence before and after drying, sucrose                                    content in Impatiens seeds, after different treatments.                                emergence   emergence                                                         before      after      sucrose                                       length of                                                                              desiccation desiccation                                                                              content before                                incubation                                                                             (moisture   (moisture  desiccation                                   treatment (d)                                                                          content 44%)                                                                              content 5%)                                                                              (% of dry weight)                             ______________________________________                                        0        98          1          0.8                                           1        97          7          1.1                                           2        98          42         2.0                                           3        96          87         2.4                                           6        98          97         3.7                                           ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Induction    Radicle Sucrose                                                                            Emergence                                           Period       Content      at 5 days                                           (days)       (% of dry weight)                                                                          (%)                                                 ______________________________________                                        0            1.56         60                                                  1            2.02         71                                                  4            3.34         98                                                  6            3.68         99                                                  ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                           Sucrose Content                                                    Drying     after Drying Emergence                                     Treatment                                                                             Rate       (%)          (%)                                           ______________________________________                                        direct  slow       4.52         96                                            drying  medium     2.96         30                                            (no     fast       1.32         1                                             incubation)                                                                   5 days  slow       5.08         98                                            incubation                                                                            medium     4.92         95                                            (before fast       4.76         96                                            drying)                                                                       ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Number of pregerminated treated Impatiens seeds out                           of 100 which form secondary roots after 14 days of incubation                 at 25° C. on moistened filter paper.                                   storage                                                                              stored at 8° C.                                                                          stored at 20° C.                              period         lot    lot              lot lot                                (months)                                                                             ctrl    1      2     ave. ctrl  1   2    ave.                          ______________________________________                                        0      99      98     98    98   98    98  98   98                            1      98      99     100   99    0    98  98   98                            2      75      100    100   100  --    98  97   97                            3      20      95     99    97   --    94  85   84                            4       0      96     94    95   --    --  --   --                            5      --      100    97    98                                                6      --      99     97    98                                                7      --      96     90    93                                                ______________________________________                                         -- = not attempted                                                       

                  TABLE 5a                                                        ______________________________________                                        Germination test on paper for seeds stored at 5 or                            19.6% moisture content                                                               % seedlings with sec                                                                           % seedlings with sec                                         roots. Seeds stored                                                                            roots Seeds stored                                    storage                                                                              at 5%            at 19.6%                                              period moisture content moisture content                                      (weeks)                                                                              -20° C.                                                                          8° C.                                                                         20° C.                                                                       -20° C.                                                                        8° C.                                                                       20° C.                      ______________________________________                                        0      --        99     --    --      99   --                                 4      99        100    100   1        0   0                                  7      98        100    98    0        0   0                                  9      98        100    99    0        0   0                                  13     98        98     98    --      --   --                                 18     100       99     99    --      --   --                                 24     92        98     90    --      --   --                                 ______________________________________                                    

                  TABLE 5b                                                        ______________________________________                                        Germination test on soil for seeds stored at 5% or                            19.6% moisture content at different temperatures                                     % seedlings      % seedlings                                           storage                                                                              (5% moisture     (19.6% moisture                                       period content)         content)                                              (weeks)                                                                              -20° C.                                                                          8° C.                                                                         20° C.                                                                       -20° C.                                                                        8° C.                                                                       20° C.                      ______________________________________                                        0      --        97     --    --      96   --                                 5      95        93     95    0        0   0                                  7      98        97     97    --      --   --                                 9      97        95     96    --      --   --                                 13     94        96     91    --      --   --                                 18     93        94     85    --      --   --                                 24     92        88     73    0        0   0                                  ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                               % seedlings for  % seedlings for                                       storage                                                                              seeds stored at 5%                                                                             seeds stored at 21.6%                                 period moisture content moisture content                                      (weeks)                                                                              -20° C.                                                                          8° C.                                                                         20° C.                                                                       -20° C.                                                                        8° C.                                                                       20° C.                      ______________________________________                                        0      --        90     --    --      89   --                                 2      --        90     --    --      49   --                                 8      93        91     95    12       2   2                                  12     90        90     90     8       4   0                                  16     91        91     93     2       1   0                                  24     94        94     93    --      --   --                                 ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Percentage of plants obtained after sowing treated                            Brussels sprouts seeds in soil.                                                      seeds at 20.9%   seeds at 5%                                           storage                                                                              seed moisture    seed moisture                                         period storage temperature (°C.)                                                               storage temperature (°C.)                      (months)                                                                             -20      8       20    -20    8     20                                 ______________________________________                                        0      94       94      94    92     92    92                                 1      34       78      2     94     90    86                                 2      20       74      0     94     94    90                                 ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Time on                 Seeds with Des.                                       sowing Non-treated      tol. emerged                                          simulator                                                                            seeds            radicles                                              (mins) % moisture emergence % moisture                                                                             emergence                                ______________________________________                                        0      45.9       96        44.3     95                                       30     32.7       97        33.7     94                                       60     19.8       97        21.3     93                                       120    8.0        65        8.1      93                                       180    6.1        63        6.5      93                                       240    6.7        50        5.7      91                                       ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                                             % of seeds showing                                              % of seeds showing                                                                          secondary root                                                  root elongation                                                                             formation 7 days/                                                                            sucrose                                          7 days/8° C./4 days                                                                  8° C./4 days water                                                                    content                                          water imbibition                                                                            imbibition.    (μg/                                   treatment                                                                            (no drying)   (with drying)  embryo)                                   ______________________________________                                        Group 1                                                                              --            70             38.6                                      Group 2                                                                               98           76             38.4                                      Group 3                                                                              100           100            52.6                                      ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                                % seedlings                                                                             % seedlings                                                                              % Sucrose                                                                             % Sucrose                                species Untreated Treated    Before  After                                    ______________________________________                                        cucumber                                                                              8         100        3.17    10.55                                    viola   33        94         3.70     6.34                                    petunia 8         93         --      not                                                                           determined                               ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                                      %        % non-emerged                                          treatment     seedlings                                                                              seeds                                                  ______________________________________                                        Control       23       77                                                     Test          94       6                                                      ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                                % seeds with regrowth                                                                          % seeds with primary                                         of primary root  and/or secondary roots                               Treatment                                                                             after 3 days     after 8 days                                         ______________________________________                                        Portion 1                                                                             10               86                                                   (Control)                                                                     Portion 2                                                                             54               90                                                   Portion 3                                                                             72               96                                                   ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                               Length of emerged radicle                                                     0.5-1.5 mm    1.5-2.5 mm                                                             Secondary           Secondary                                                 root                root                                                      formation           formation                                          Primary                                                                              from       Primary  from                                               root   hypocotyl  root     hypocotyl                                          survival                                                                             region     survival region                                             (3 days)                                                                             (7 days)   (3 days) (7 days)                                    ______________________________________                                        Control  37       85         0      64                                        PEG      97       100        37     100                                       Paclo-   97       100        83     100                                       butrazol                                                                      plus PEG                                                                      ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        Percentage of seeds developing into seedlings                                 14 days after sowing.                                                                (% of dry weight)                                                               hypocotyl     cotyledon                                                       sucrose       sucrose   %                                            treatment                                                                              content       content   seedlings                                    ______________________________________                                        control  0.70          0.57      2                                            1d PEG   4.23          1.93      68                                           2d PEG   4.82          2.15      75                                           5d PEG   7.40          2.74      96                                           ______________________________________                                    

We claim:
 1. Pregerminated seeds comprising desiccation tolerant emergedradicles wherein the emerged radicles contain elevated levels of sucroserelative to non-desiccation tolerant emerged radicles of the same plantspecies and wherein said desiccation tolerant seeds have an overallmoisture content in the range of about 35% to about 55% by weight of theseeds and are capable of resuming growth when planted.
 2. Pregerminatedseeds according to claim 1 wherein said seeds have been stored atambient storage conditions.
 3. Pregerminated seeds comprisingdesiccation tolerant emerged radicles wherein the emerged radiclescontain elevated levels of sucrose relative to non-desiccation tolerantemerged radicles of the same plant species and the moisture content ofsaid desiccation tolerant seeds lies in the range of about 4% to about12% by weight of the seeds and are capable of resuming growth whenplanted.
 4. Pregerminated seeds according to claim 1 wherein the seedsare selected from plants of the group consisting of Alliums,Antirrhinums, Begonias, Brassicaceae, Capsicums, Cucurbitaceae,Lycopersicons, Cyclamens, Betas, Dianthuses, Gazanias, Gerberas,Impatiens, Lobelias, Nicotianas, Pelargoniums, Petunias, Phloxes,Primulas, Raphanuses, Salvias, Solanums, Tagetes, Verbenas, Vincas,Violas, Apiums, Chicoriums, Daucuses and Zinnias.
 5. Pregerminated seedsaccording to claim 1 further comprising a seed coating.
 6. Pregerminatedseeds according to claim 1 wherein the desiccation tolerance is locatedin the hypocotyl region of the radicle.
 7. Pregerminated seeds accordingto claim 3 wherein the seeds are selected from the group consisting of,Allium, Antirrhinums, Begonias, Brassicaceeae, Capsicums, Cucurbitaceae,Lycopersicons, Cyclamens, Betas, Dianthuses, Gazanias, Gerberas,Impatiens, Lobelias, Nicotianas, Pelargoniums, Petunias, Phloxes,Primulas, Raphanuses. Salvias, Solanums, Tagetas, Verbenas, Vincas,Apiums, Chicoriums, Daucuses, and Violas.
 8. Pregerminated seedsaccording to claim 3 further comprising a seed coating.
 9. Pregerminatedseeds according to claim 3 wherein the seeds are Impatiens seeds. 10.Pregerminated seeds according to claim 3 wherein the seeds are Pansyseeds.
 11. Pregerminated seeds comprising desiccation tolerant emergedradicles and having an overall moisture content in the range of about35% to about 55% by weight of the seed wherein the embryos of the seedhave an elevated sucrose level relative to the embryos of pregerminatedseeds with non-desiccation tolerant emerged radicles of the same plantspecies.
 12. Pregerminated seeds comprising desiccation tolerant emergedradicles wherein the moisture content of said seeds is in the range ofabout 4% to about 12% wherein the embryos of the desiccation tolerantseeds have an elevated sucrose level relative to the embryos ofpregerminated seeds with non-desiccation tolerant emerged radicles ofthe same plant species.
 13. Pregerminated seeds according to claim 11wherein the seeds are salaried from the group of seeds consisting ofImpatiens, Viola, Pansy and Cyclamen.
 14. Pregerminated seeds accordingto claim 12 wherein the seeds are selected from the group of seedsconsisting of Impatiens, Viola, Pansy and Cyclamen.
 15. Pregerminatedseeds according to claim 1 wherein the seeds are Impatiens seeds. 16.Pregerminated seeds according to claim 3 wherein said seeds have beenstored at ambient storage conditions.
 17. Pregerminated seeds accordingto claim 3 wherein the desiccation tolerance is located in the hypocotylregion of the radicle.